As is well known to those skilled in this art, Parkinson's disease is a degenerative brain disorder of the nonvascular system which is the next most common after senile dementia. This disease is very prevalent among the elderly. As the elderly population increases, the rate of incidence of this disease is concomitantly increasing. Although the pathogenesis of Parkinson's disease has not yet been clearly determined, a lack of dopamine which is a kind of neurotransmitter is known to be an immediate cause of this disease. This causes different kinds of dyskinesia such as hand tremors or bradykinesia. Up to now, a fundamental therapy has not yet been discovered.
Methods of treating Parkinson's disease, for example, include drug treatments for supplementing insufficient dopamine, and surgery which completely removes a brain structure that is malfunctioning attributable to the lack of dopamine. Recently, a method for treating dyskinesia was disclosed, in which fine thin electrodes are inserted into deep brain structures such as the thalamus, globus pallidus and subthalamus and then electric stimulation is applied thereto. An apparatus that is used in this method is called a deep brain stimulator (DBS). A representative example of the DBS was proposed in US patent No. 2006/0184209, which was filed by Constance M. John, etc. on Aug. 17, 2006 and entitled “DEVICE FOR BRAIN STIMULATION USING RF ENERGY HARVESTING”.
Advantages of this deep brain stimulation method are that compared to drub treatment or surgery, the remedial effects are superior, the risk of brain damage is low, and it is not required to remove brain tissues. Therefore, this method is receiving much attention as a new therapy. Improvements in relieving the symptoms of Parkinson's disease using such a DBS are comparatively superior and satisfactory to 90%. The use of DBS was permitted by the FDA (Food and Drug Administration). According to a report of the NIH (National Institutes of Health), more than 2000 patients underwent a DBS transplant operation.
However, DBSs that are being transplanted have to overcome problems of a limited battery life which causes frequent replacement of the DBS, its large size making the surgery complex, etc. Next-generation DBSs that overcome these problems are being actively developed. To prove the effectiveness of developed DBSs and increase the range of application of the DBSs (e.g. to apply the DBSs to treatments for pain, epilepsy, etc.), animal testing (using animals, only one half of the brain to which a Parkinson's disease lesion is applied) is proceeding.
In the animal tests using the DBSs, because animal models must be biologically safe, the DBSs must have no effect on living bodies, stimulation electrodes or electric stimulation must not cause brain cell destruction, and the material used to make the stimulation electrodes must be biocompatible. To conduct deep brain stimulation therapy, the precise location of a lesion in the deep structure of the brain must be determined. For this, images using MRI (magnetic resonance imaging) and fine electrodes are used in combination, markedly enhancing the degree of precision of location setting and the surgery.
A fine electrode which can record nerve signals from the deep structures of the brain is formed such that the end thereof is sharp. Further, in the metal electrode that is used, all parts of it except for a nerve signal measuring part are insulated. Such a fine metal electrode is manufactured in such a way that an insulation film is applied to a metal wire that has a pointed end and then a portion of the insulation film that corresponds to the pointed end is removed so that the metal of the nerve signal measuring part is exposed to the outside from the insulation film. However, because the deep brain stimulation therapy aims to measure nerve signals from a single nerve cell, only about several μm of the metal of the nerve signal measuring part must be exposed to the outside. Depending on the purpose, in other words, whether it is for blood vessels or spines, a plurality of platinum rings must be provided at regular intervals.
In the above-stated conventional fine electrodes, the material of the electrode is platinum, it is very thin, and several electrodes are longitudinally arranged in a line. Therefore, the electrode basically has low tensile strength. Thus, if a force or impact is longitudinally applied to the electrode, it easily snaps.
To overcome these problems, electrodes may be manufactured in such a way that they are twisted to form a helical shape. However, in this case, there is a likelihood of the electrodes becoming tangled. If the electrodes are tangled, the tangled portion also easily snaps when force is longitudinally applied thereto.